Subsequent Events (Details) (2014 Acquisitions [Member], USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended			1 Months Ended
	Jun. 30, 2014 property sqft		Jun. 30, 2013 property	Jun. 30, 2014 property sqft		Jun. 30, 2013 property	Jul. 28, 2014 Subsequent Event [Member] sqft property
Number of Buildings [Roll Forward]
Number of properties acquired	122		899	337		1,011	586
Number of owned properties	3,966			3,966			4,552
Area of Acquisitions [Roll Forward]
Square Feet, Acquisitions							5,200,000
Square feet of property	106,800,000			106,800,000			112,000,000
Purchase Price of Acquisitions [Roll Forward]
Base Purchase Price, Acquisitions							$ 1,939	[1]
Base Purchase Price	$ 17,831	[1]		$ 17,831	[1]		$ 19,770	[1]

[1] Contract purchase price, excluding acquisition and transaction related costs.